The present invention relates to a nuclear fuel element and, more particularly, to a nuclear fuel element suitable for use in a fast breeder.
Generally, a fast breeder has a core loaded with fuel assemblies each having a wrapper tube of a hexagonal cross-section and a multiplicity of fuel pins which are the nuclear fuel elements. The fuel pin has a clad tube closed at its both ends by end plugs, a multiplicity of fuel pellets charged in the clad tube and a wire spacer spirally wound round the clad tube. The wire spacer is fixed at its both ends to the end plugs closing the ends of the clad tube. A gas plenum is formed within the clad tube at a lower portion of the fuel pin. An intermediate plug is disposed at the boundary between the gas plenum and the region charged with pellets. The intermediate plug is a porous member which is attached to the clad tube. The core of the fast breeder is loaded with core fuel assemblies and blanket fuel assemblies. The pellets charged in the core fuel assemblies contain PuO.sub.2 while the pellets charged in the blanket fuel assemblies do not contain PuO.sub.2 but are composed of natural uranium or depleted uranium. Both of the core fuel assemblies and the blanket fuel assemblies have the construction explained hereinabove.
Liquid sodium as a coolant is circulated through the wrapper tube of each fuel assembly in the reactor core. The liquid sodium, however, encounters a large resistance and, hence, a large pressure drop is caused because wire spacers are wound round numerous fuel pins.